Electrodeposition of nickel



United States Patent Ofifice 3,3 12,604 Patented Apr. 4, 1967 3,312,604ELECTRODEPOSITION F NICKEL Frederick Herbert Wells, Sutton Coldfield,and Peter John Worrall, Kidderminster, England, assignors to Albrrght &Wilson (Mfg.) Limited, Oldbury, Warwickshu'e, England, a British companyNo Drawing. Filed Oct. 22, 1963, Ser. No. 318,109 Claims priority,application Great Britain, Oct. 25, 1962, 40,384/62; June 17, 1963,23,987/63 12 Claims. (Cl. 204-49) This invention relates to theelectrodeposition of nickel. It is an object of the invention to provideon a basis metal a nickel electrodeposit having a satin-like finish,that is a surface which exhibts a lustrous sheen and, although bright,gives a difiuse image lacking in contrast when used as a reflectingsurface. Such a finish is desirable as a decorative finish for manyarticles but also I as a basis electrodeposit to which there issubsequently to be applied a chromium or other further electrodeposit toprovide the article with an extremely hard-wearing, smooth and brightsurface.

Hitherto, a satin-like finish has been provided by mechanical treatmentof the basis metal to alter its surface prior to electrodeposition ofthe nickel, or by sand, shot or vapour blasting of the surface of thenickel plated article.

We have now found that a nickel electrodeposit having a pleasingsatin-like finish can be obtained by using an aqueous nickel electrolytewhich comprises nickel sulphate and a levelling agent and to which hasbeen added a small quantity of a water-soluble strontium salt. Such anelectrolyte provides the desired satin-like finish without requiringspecial filtration equipment or agitation of the electrolyte during use.We have tried to produce a similar effect by the analogous use of awater-soluble calcium salt but without success and in our experiencesatisfactory electrodeposition to produce a satin-like finish using aWater-soluble barium salt as additive to the electrolyte is onlyobtained if the electrolyte is vigorously agitated using a specialdevice in order to disperse the precipitated barium sulphate. The needto use such agitation renders the operation of the process undulycomplex.

Accordingly, the present invention provides an aqueous electrolyte forthe electrodeposition of nickel, which comprises nickel sulphate, alevelling agent (as hereinafter defined) and from parts per million to 1gram per liter of strontium which has been added to the electrolyte inthe form of a water-soluble salt thereof.

The invention also provides a process for the electrodeposition ofnickel which comprises employing therein an electrolyte of theinvention. The invention further provides articles having a nickelelectrodeposit Whenever obtained by such a process.

The electrolyte of the invention comprises nickel sulphate. This may bethe sole nickel salt in the electrolyte or there may be present alsoother nickel salts, for instance nickel chloride, fluo-borate and/orsulphamate. The total content of nickel is such as to provide aconcentration of nickel between 16 and 400 grams per liter, preferablybetween 70 and 120 grams per liter. A particularly suitable electrolyteis one known commercially as the Watts bath. The modern variation ofthis contains nickel sulphate in a concentration of about 200-450 gramsper liter (calculated as the hexahydrate) and nickel chloride in aconcentration of 3060 grams per liter (calculated as the hexahydrate).The Watts bath also contains boric acid in a concentration of from 30 to50 grams per liter. The present process can also be operated with anelectrolyte in which the nickel chloride content is equal to or greaterthan the nickel sulphate content.

The present electrolyte also often contains other inorganic constituentsin addition to the nickel salt or salts. Thus, there may be present oneor more of the following: boric acid; ammonium salts such as ammonium ornickel ammonium sulphate; sodium sulphate, magnesium sulphate, Zincsulphate, sodium thiocyanate, acetic acid, sulphamic acid, hydrochloricacid, fluoboric acid or sulphuric acid.

The water-soluble strontium salt added to the electrolyte is usuallystrontium chloride or nitrate.

The concentration of strontium provided in the electrolyte by thisaddition may vary from 10 parts per million to 1 gram per liter(calculated as strontium), but it is preferred that the concentrationshould not exceed 500 parts per million.

To provide the desired satin finish to the electrodeposit it isnecessary that the electroylte also contain a levelling agent, that isan agent which causes the electrodeposit formed to be of varyingthickness and to exhibit a level surface despite minor undulations inthe surface of the basis metal. Any compound, the presence of whichresults in an electrodeposit more smooth than the surface of the basismetal, is herein termed a levelling agent. Many such agents are knownfor use in nickel plating electrolytes and they include coumarin,substituted coumarins such as alkyl-, alkoxyand halo-coumarins,p-sulphocinnamic acid, o-hydroxycinnamic acid, acetylenic compounds,thiourea and nitrogen-heterocyclic amines such as quinoline,isoquinoline and quinaldine compounds. There may also be employedprecursors of such compounds, that is compounds which react to form alevelling agent under the conditions of operation for the electrolyte.

Many of the known levelling agents also function as brightening agents,that is the surface of the resulting electrodeposit exhibits a greaterreflectance than when the agent is omitted from the electrolyte. Thus anagent which is at the same time a good levelling and brightening agentwill impart specularity to the electrodeposit. However, specularity isnot desired of the present invention and therefore levelling agentswhich are also among the most efiective of the brightening agents aremuch less preferred in the present invention since the brighteningeffect tends to supercede the satin-finish which is then only obtainedon localized areas of the electrodeposit. Thus we have found that onlymarginally successful results of uniform satin-like finish to theelectrodeposit are obtained when the present electrolytes containacetylenic alcohols, such as butyn-l, 4-diol, or thiourea as thelevelling agent since these are also brightening agents of highefliciency. The preferred levelling agents for present use are thereforeonly moderately-active brightening agents. The levelling agent maybeemployed in the concentration conventional to its use for this purpose.

A particularly preferred levelling agent for present use is coumarin ora substituted coumarin. For such a levelling agent the optimumconcentration is from 0.1 to 0.5 gram per liter. Another particularlypreferred levelling agent for present use is o-benzaldehyde sulphonicacid or a Water-soluble salt thereof, especially in its optimumconcentration of from 0.1 to 5 grams per liter. If desired, mixtures oflevelling agents may be present provided that they do not provide toogreat a degree of brightening to the electrodeposit. Thus, mixtures ofo-benzalde'hy-de sulphonic acid or a salt thereof and coumann or asubstituted coumarin may be employed, if desired.

The electrolyte of the invention preferably also contams a carrierbrightener to relieve any stress in the electrodeposit. These carrierbrighteners are usually organic sulpho-oxygen compounds and do not, ingeneral, also act as levelling agents. However, o-benzaldehyde sulphonicacid is also a levelling agent so that when it is present in theelectrolyte of the invention no other carrier brightener needs to bepresent to relieve stress in the electrodeposit, though, if desired,some other organic sulphooxygen compound may be present as an additionalcarrier brightener. As carrier brighteners there may be used, for1nstance, aromatic or unsaturated aliphatic sulphonic acids,sulphonamides or sulphonimides, for example a naphthalenesulphonic acid,allyl sulphonic acid or saccharin. The sulphonic acids are oftenconveniently added to the electrolyte in the form of their sodium salts.The preferred additive of this type for present use is anaphthalenetrisulphonic acid, particularly 1,3,6-naphthalenetrisulphonicacid. The carrier brightner may be present in any concentration up tosaturation, but a concentration of from 1 to 10 grams per liter usuallyprovides optimum results. Particularly advantageous results are obtainedwhen the present electrolytes contain either o-benzaldehyde sulphonicacid or a water-soluble salt thereof as combined levelling agent andcarrier brightener, or the combination of a coumarin compound as thelevelling agent and a sulpho-oxygen compound as carrier brightener,especially the combination of coumarin. and1,3,6-naphthalenetrisulphonic acid in the above-mentioned preferredproportions.

The present electrolytes also often contain surfaceactive agents,particularly those of the anionic or non-' ionic type. For instancethere may be present up to 5 grams per liter, usually not more than 1gram per liter, of such agents, particularly of sodium lauryl sulphateor a lauryl-, octylphenylor nonylphenyl-polyethylene ether alcohol.

The electrolytes of the invention normally have a pH value of less than7, that is they are acidic electrolytes; preferably the presentelectrolyte has a pH value of at least 1.5 and particularly of 2.7-4.5.

The present process is a conventional one of electrodeposition of nickelusing one or more anodes, which may be of nickel or of an inert materialsuch as carbon, and making the article to be plated the cathode in thesystem, but in which the electrolyte employed is an electrolyteaccording to the present invention. However, best results are obtainedfrom the process of the invention if it is operated at a moderately highor high current density, that is a current density of at least amps persquare foot; the preferred current density for present use is one from20 to 60 amps per square foot. The process of the invention is normallyoperated with a warm electrolyte, for example, at a temperature of from30 to 60 C., though temperatures between 0 C. and 100 C. can be used ifdesired. The process may be carried out for any convenient period, butusually a period of from 5 to 60 minutes is sufficient to provide thepreferred thickness of electrodeposit which is from 0.0001 to 0.001inch. Greater thicknesses are possible. If desired, mild air-agitationof the electrolyte may be carried out during the electrodeposition, butsuch agitation is by no means essential and, if excessive, results inbright patches being obtained on the electrodeposit which, otherwise,has a satin-like finish. Indeed agitation of the electrolyte during useis preferabl yto be avoided.

After electrodeposition has been completed the plated article is washedand dried. This article has a very pleasing satin-like finish, and, ifdesired, may readily be polished to provide a two tone effect, that isby mechanical polishing of only part of the surface of the article towhich has previously been imparted the satin-like finish.

Particularly useful results are obtained from the present invention if,after the satin-like nickel electrodeposit has been applied, the articleis transferred to a second electrolyte and subjected to a furtherelectrodeposition process, particularly chromium electrodeposition. Achromi urn-plated article prepared in this manner has an electrodepositof chromium, whose surface is very bright and hard wearing and whoseadherence to the basis metal is enhanced by the intervening nickelelectrodeposit with the satin-like finish provided by the presentinvention. Such a combined electrodeposit has been shown to have aparticularly high corrosion resistance.

The invention will now be illustrated by the following1,3,6-naphthalenetrisulphonic acid (sodium salt) 2.0

The electrolyte was used to provide electrodeposits of nickel on testpieces of polished zinc alloy, brass and steel. The electrolyte was usedat 60 C. employing a current density of 60 amps per square foot. After20 minutes the panels were removed from the electrolyte and found topossess a nickel deposit of 0.001 inch thickness having a satin-likesurface finish of high luster and sheen.

Example 2 A further sample was plated using an electrolyte of pH 3.5having the composition:

Concentration (grams per liter) Nickel sulphate (NiSO .6H O) 312 Nickelchloride (NiCl .6H O) 78 Boric acid 43 1,3,6-naphthalenetrisulphonicacid (sodium salt) 1 Coumarin 0.2 0.5

Strontium chloride The sample plated was a polished zinc-alloydiecasting that had been given an initial electrodeposit of copper whichwas then followed by a satin-like nickel coating from the abovementioned bath. The thickness of the nickel coating was 0.00025 inch andwas obtained by plating at 60 amps/sq. ft. for 5 minutes; the bathtemperature was 50.

The nickel-plated die-casting was then itself used as basis -metal andan electrodeposit of chromium applied from a high temperature high ratiochromium electrolyte having a ratio of CrO to H 50 of -150z1 by weightemploying a current density of about 300 amps/ sq. ft. at 55 C. Therewas obtained an electrodeposit of chromium which was extremely hard andvery adherent to the underlying electrodeposit.

Example 3 An electrolyte of pH 4.5 was prepared of the composition:

Concentration (grams per liter) Nickel sulphate (NiSO .6H O) 312 Nickelchloride (NiCl .6l-I O) 78 Boric acid 43 1,3,6-naphthalenetrisulphonicacid (sodium salt) 6 Sodium lauryl sulphate 0.4

Coumarin 0.2

Strontium chloride 0.1

This electrolyte was employed to provide an electrodeposit of nickel ofthickness 0.0005 inch having a satin finish on a zinc alloy diecastingto which had previously been applied an electrodeposit of copper. Thetemperature of the electrolyte was 60 C. and a current density of 30amps/ sq. ft. was applied for 20 minutes.

To this nickel plated diecasting there was then applied a chromiumelectrodeposit as described in Example 2 which again exhibited theproperties of high adherence and hardness.

Example 4 To an electrolyte of the Watts bath type having thecomposition there were added 20 parts per million of strontium chloride,0.5 gram per liter of sodium o-benzaldehyde sulphonate and 100 parts permillion of sodium lauryl sulphate as surface-active agent. The resultingelectrolyte had a pH value of from 3.0 to 3.5.

This electrolyte was used to provide electrodeposits of nickel on testpieces of polished zinc alloy, brass and steel. The electrolyte wasemployed at 35-45 C. without agitation and a current density of 50 ampsper square foot. After 12 minutes the panels were removed from theelectrolyte and found to possess a nickel deposit of 0.0005 inchthickness having a uniform satin-like surface finish of high luster andsheen.

Example 5 To an electrolyte of the Watts bath type having thecomposition there were added: 30 parts per million of stronium chloride,0.5 gram per liter of sodium o-benzaldehyde sulphonate and 100 parts permillion of sodium lauryl sulphate. The pH value of the resultingelectrolyte was 3.5 and it was operated at a temperature between 40 and50 C.

This electrolyte was used to provide electrodeposits of nickel on testpieces of gilding metal and brass. At a current density of 50 amps persquare foot a deposit thickness of 0.00025 inch was produced in 6minutes Without agitation of the electrolyte. The surface had a uniformsatin-like appearance of high luster.

Example 6 A satisfactory nickel electrodeposit having a satin-likesurface of high luster and sheen was obtained when EX- ample 1 wasrepeated with the electrolyte therein used, but in which thenapthalenetrisulphonate had been replaced by either saccharin orp-toluenesulphonamide, each in a concentration of 2 grams per lite-r.

Example 7 An electrolyte containing at least the same concentration ofnickel chloride as nickle sulphate was prepared and had the composition:

Nickel sulphate (NiSO .6H O) grams per liter 150 Nickel Chloride (NiCl.6H O) do 150 Boric acid do 35 Coumarin do 0.2 Strontium chloride -partsper million 30 Sodium 1,3,6-naphthalenetrisulphonate,

grams per liter 1 concentration of nickel sulphate varied between and200 grams per liter.

What we claim is:

1. In an acidic aqueous electrolyte for the electrodeposition of nicklewhich comprises nickel sulphate and a nickel electrodeposition levellingagent, the improvement which consists in there having been added to saidelectrolyte a water-soluble salt of strontium in an amount within therange of 10 parts per million to 1 gram per liter (calculated asstrontium), whereby the electrolyte maybe operated to provide a nickelelectrodeposit having a satin-like finish.

2. In an acidic aqueous electrolyte for the electrodeposition of nickelwhich comprises nickel sulphate and a nickel electrodeposition levellingagent selected "from the group consisting of coumarin, alkyl-coumarins,alkoxycoumarins, halo coumarins, o benzaldehydesulphonic acid andwater-soluble o-benzaldehydesulphonate salts, the improvement whichconsists in there having been added to said electrolyte a water-solublesalt of strontium in an amount within the range of 10 parts per millionto 1 gram per liter (calculated as strontium), whereby the electrolytemay be operated to provide a nickel electrodeposit having a satin-likefinish.

3. In an acidic aqueous electrolyte of the Watts type for theelectrodeposition of nickel which comprises nickel sulphate in an amountof from 200 to 400 grams per liter (calculated as the hexahydrate),nickel chloride in an amount of from 30 to 60 grams per liter(calculated as the hexahydrate), boric acid in an amount of from 30 to50 grams per liter, and a nickel electrodeposit levelling agent which isat best a moderately-active brightening agent, the improvement whichconsists in there having been added to said electrolyte a water-solublesalt of strontium in an amount within the range of 10 parts per millionto 1 gram per liter (calculated as strontium), whereby the electrolytemay be operated to provide a nickle electrodeposit having a satin-likefinish.

4. In an aqueous electrolyte of the Watts typ'e for theelectrodeposition of nickel which has a pH value within the range 2.7 to4.5 and which comprises nickel sulphate in an amount of from 200 to 400grams per liter (calculated as the heXahyd-rate), nickel chloride in anamount of from 30 to 60 grams per liter (calculated as the hexahydrate),boric acid in an amount of from 30 to 50 grams per liter, an organicsulpho-oxygen compound as carrier brightener and a nickelelectrodeposition levelling agent selected from the group consisting ofcoumarin, alkylcoumarins, alkoXy-coumarins, halo-coumarins,o-benzaldehydcsulphonic acid and water-soluble o-benzaldehydesulphonatesalts, the improvement which consists in there having been added to saidelectrolyte a water-soluble salt of strontium in an amount within therange of 10 parts per million to 1 gram per liter (calculated asstrontium), whereby the eelct-rolyte may be operated to provide a nickelelectrodeposit having a satin-like finish.

5. In an aqueous electrolyte of the Watts type for the electrodepositionof nickel which has a pH value within the mange 2.7 to 4.5 and whichcomprises nickel sulphate in an amount of from 200 to 400 grams perliter (calculated as time hex athy dmate), nickel chloride in an amountof from 30 to 60 grams per liter (calculated as the hexahydrate), boricacid in an amount of from 30 to 50 grams per liter, an organicsulpho-oxygen compound as carrier brightener and, as nickel electrodeposition leveling agent, coumatrin in an amount of from 0.1 to 0.5 gramper liter, the improvement which consists in there having been added tosaid electrolyte a watersoluble salt of strontium in an amount withinthe range of 10 per million to 1 gram per liter (calculated asstrontium), whereby the electrolyte may be operated to provide a nickelelectrodeposit having a satin-like finish.

6. In an aqueous electrolyte of the Watts type for the electrodepositionof nickel which as a pH value within the range 2.7 to 4.5 and whichcomprises nickel sulphate in an amount of from 200 to; 400 grams perliter (calculated as the hexahydrate), nickel chloride in an amount offrom 30 to 60 grams per liter (calculated as the hexahydrate), boricacid in an amount of from 30 to 50 grams per liter, an organicsulpho-oxygen compound as carrier brightener and, as nickelelectrodeposition levelling agent, o-benzaldehydesulphonic acid in anamount of from 0.1 to grams per liter, the improvement which consists inthere having been added to said electrolyte water-soluble salt ofstrontium in an amount within the range of parts per million to 1 gramper liter (calculated as strontium), whereby the electrolyte may beoperated to provide a nickel electrode-posit having a satin-like finish.

7. In a process for the electrodeposition of nickel on a cathode whereinthere is employed an acidic aqueous electrolyte which comprises nickelsulphate and a nickel electrodeposition levelling agent, the improvementwhich consists in there having been added to said electrolyte awater-soluble salt of strontium in an amount within the range of 10parts per million to 1 gram per liter (calculated as strontium), wherebythere is obtained a nickel electrodeposit having a satin-like finish.

8. In a process for the electrodeposition of nickel on a cathode whereinthere is employed an acidic aqueous electrolyte which comprises nickelsulphate and a nickel electrodeposition levelling agent, the improvementwhich consists in there having been added to said electrolyte awater-soluble salt of strontium in an amount within the range of 10parts per million to 1 gram per liter (calculated as strontium) and inoperating the said process without agitation of the said electrolyte,whereby there is obtained a nickel electrodeposit having a satinlikefinish.

9. In a process for the electrodeposition of nickel on a cathode whereinthere is employed an acidic aqueous electrolyte which comprises nickelsulphate in an amount of from 200 to 400 grams per liter (calculated asthe hexahydrate), nickel chloride in an amount of from 30 to 60 gramsper liter (calculated as the hexahydrate), boric acid in an amount offrom 30 to 50 grams per liter, and a nickel electrodeposit levellingagent which is at best a moderately-active brightening agent, theimprovement which consists in a there having been added to saidelectorlyte a water-soluble salt of strontium in an amount within therange of 10 parts per million to 1 gram per liter (calculated asstrontium), whereby there is obtained a nickel electrodeposit having asatin-like finish.

10. In a process for the electrodeposition of nickel on a cathode thereisemployed an aqueous electrolyte having a pH value within the range 2.7to 4.5 and which comprises nickel sulphate in an amount of from 200 to400 grams per liter (calculated as the hexahydrate), nickel chloride inan amount of from 30 to 60 grams per liter (calculated as thehexahydrate), boric acid in an amount of from 30 to 50 grams per liter,an organic sulpho-oxygen compound as carrier brightener and a nickelelectrodeposition levelling agent selected from the group consisting ofcournarin, alkyl-coumarins, alkoxyooumarins, hialoeoum arins, obenzialdehydesulphionic acid and water-soluble o-benzaldehydesulphonatesalts, the improvement which consists in there having been added to saidelectrolyte a water-soluble salt of strontium in an amount within therange of 10 parts per million to 1 gram per liter (calculated asstrontium) land in operating the said process without agitation of thesaid electrolyte, whereby there is obtained a nickel electrodeposithaving a satin-like finish.

11. In a process for the electrodeposition of nickel on a cathodewherein there is employed an aqueous electrolyte having pH value withinthe range 2.7 to 4.5 and which comprises nickel sulphate in an amount offrom 200 to 400 grams per liter (calculated as the hexahydrate), nickelchloride in an amount of from 30 to grams per liter (calculated as thehexahydrate), boric acid in an amount of from 30 to 50 grams per liter,an organic sulpho-oxygen compound as carrier brightener and, as nickelelectrodepositionlevelling agent, coumarin in an amount of from 0.1 to0.5 gram per liter, the improvement which consists in there having beenadded to said electrolyte a water-soluble salt of strontium in an amountwithin the range of 10 parts per million to 1 gram per liter (calculatedas strontium) (and in openating the said process without agitation ofthe said electrolyte, whereby there is obtained a nickel electrodeposithaving a satin-like finish.

12. In a process for the electrodeposition of nickel on a cathodewherein there is employed an aqueous electrolyte having a pH valuewithin the range 2.7 to 4.5 and which comprises nickel sulphate in anamount of from 200 to 400 grams per liter (calculated as thehexahydrate), grams per liter (calculated as the hexahydrate), boricacid in an amount of from 30 to 50 grams per liter, an organicsulpho-oxygen compound as carrier brightener and, as nickelelectrodeposition levelling agent, o-benzaldehydesulphonic acid in anamount of 0.1 to 5 grams per liter, the improvement which consists inthere having been added to said electrolyte a water-soluble salt ofstrontium in an amount within the range of 10 parts per million to 1gram per liter (calculated as strontium) and in operating the saidprocess without agitation of the said electrolyte at a current densityof fiI'OIIl 20 to 60 amps per square foot, whereby there is obtained anickel electrodeposit having a satin-like finish.

References Cited by the Examiner UNITED STATES PATENTS 3,130,135 4/1964Ericson 204-49 JOHN H. MACK, Primary Examiner. G. KAPLAN, AssistantExaminer.

nickel chloride in an amount of from 30 to 60

1. IN AN ACIDIC AQUEOUS ELECTROLYTE FOR THE ELECTRODEPOSITION OF NICKLEWHICH COMPRISES NICLEL SULPHATE AND A NICKEL ELECTRODEPOSTION LEVELLINGAGENT, THE IMPROVEMENT WHICH CONSISTS IN THERE HAVING BEEN ADDED TO SAIDELECTROLYTE A WATER-SOLUBLE SALT OF STRONTIUM IN AN AMOUNT WITHIN THERANGE OF 10 PARTS PER MILLION TO 1 GRAM PER LITER (CALCULATED ASSTRONTIUM), WHEREBY THE ELECTROLYTE MAY BE OPERATED TO PROVIDE A NICKELELECTRODEPOSIT HAVING A SATIN-LIKE FINISH.